In the past, as image capture devices, there have been known image capture devices having a lens that is movable in the optical axis direction and an imaging element that receives light through lenses. Such image capture devices are configured such that the autofocus control, which controls the position of the lens in a stepwise fashion, can be executed in order to obtain image capturing data for each field of the focus areas. As the lens moves, a decrease in a focus estimation value, for example, a detected contrast value is checked, thereby recognizing the position of the lens at the focus estimation value, from which the decrease starts, as a target lens position. Such image capture devices employ an actuator using shape-memory alloy in order to move a driven section which has the lens (for example, refer to Patent Literature 1 to 3).
The shape-memory alloy used in the actuator has, for example, a wire shape, and thus its shape is changeable in the lengthwise direction. When the shape-memory alloy is heated up, the temperature thereof increases, and the alloy contracts in the lengthwise direction. In contrast, when the shape-memory alloy is cooled down, the temperature thereof decreases, and the alloy extends in the lengthwise direction.
By using an actuator using the shape-memory alloy with such a characteristic and an urging member, the position of the driven section is controlled. For example, a position (a ZERO position), where the shape-memory alloy to which current is not applied and which is not heated to be at the room temperature holds the position of the driven section against elastic force generated by the urging member, is set as a position closer to the imaging element side than the position at infinity. By applying current to the shape-memory alloy so as to heat the alloy, in the actuator, the shape-memory alloy contracts in the lengthwise direction, thereby maximally moving the driven section from the ZERO position to the closest point position. Next, in a case where the driven section is returned to the ZERO position again, the actuator stops the heating by shutting off the current application to the shape-memory alloy and so on, and naturally dissipates the heat and so on, thereby cooling down the shape-memory alloy. In such a manner, the shape-memory alloy extends in the lengthwise direction, thereby moving the driven section to the ZERO position against the elastic force generated by the urging member.
However, in the conventional image capture device, in a case where the driven section is moved to a prescribed position and thereafter the driven section is moved to another position, by cooling down the shape-memory alloy, the driven section is moved to the ZERO position, and then by heating up the shape-memory alloy, the driven section is moved to another position. Accordingly, in the conventional image capture device, when the driven section is moved from the prescribed position to another position, it passes the ZERO position. Hence, in the range from the prescribed position to the ZERO position, the driven section is moved by naturally cooling down the shape-memory alloy. Accordingly, response thereof is poor, and a long time is necessary therefor.
The shape-memory alloy has problems in that, in order to move the driven section by the natural cooling, the variation in the time for the movement is caused by individual difference in the shape-memory alloy or the ambient temperature, and thus further extra time therefor is necessary.